Are You EnLIGHTENED? Pt. 1 With Dr. Glen Jeffery

April 20, 2026 Adiel Gorel

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Are You EnLIGHTENED? Pt. 1 With Dr. Glen Jeffery

Natural Vs. Artificial Light, & The Impact On Metabolic Health

It’s such a joy to be here with you again. I’m particularly excited because we have Dr. Glen Jeffery, whose name has been making the rounds in the circles of light, health, lighting, and building lightings. His research is mentioned everywhere. It’s quite a joy. Welcome to the show, Dr. Jeffery.

Thank you very much. It’s a pleasure to be here.

I’m going to take the liberty of calling you Glen.

Please do. I much prefer it.

How Glen Started To Study And Research About Light

Glen, before we even get started and get into the meat of what we’re going to talk about, can you give us just the trajectory that took you to this point?

It’s a nonlinear progression. I did my first degree in Experimental Psychology in a time when there was a lot of physiology and a lot of maths. I did my PhD in Vision. I’ve spent most of my career looking at the eye and the visual brain and visual perception. I had no idea about anything about environmental light. Certainly, I didn’t know what mitochondria was. I didn’t have a very strong biology background.

I started reading a few papers that led me towards thinking more about, not necessarily about the visual brain, but how humans as an organism respond to light. That’s great because there was then a very significant career change in terms of my trajectory. There was a very different collection of people around me. Surprisingly, people interested in vision are not desperately interested in light.

People interested in light are publishers, artists, architects. I suddenly found out that a lot of science was very heavily siloed. I was in one silo. The people that I wanted to talk to were in another silo. Breaking down those silos was a major change in my life. I still got one foot in the visual brain. My other foot is somewhere probably lost in an architect’s office or an astronomer’s office or something like that. That’s roughly why I’ve ended up where I am.

The mention of the word silo is part of the problem that I see. People are great experts in a very narrow silo. The walls are preventing them. They don’t even have an inclination to check on the other side. In an ideal way, in an ideal world, you’d have a group of people come together and share. That’s not easy. That’s why I like the little group that you have with Scott Zimmerman and Bob Fosbury. Right there, already, you touch upon several branches of science at the same time.

We’ve got Bob Fosbury, who’s a world leader in understanding atmospheric light very much in exoplanets many millions of miles away. Scott, who’s basically an electrical engineer. The silos came down between us. The one that kicked the silos heavily was Bob. Bob was the one who first jumped. He walked into my lab, having retired, being very fed up.

He said, “Can we do something together?” In reality, I knew nothing about light. I’m not sure I know a lot. The silo issue is one of the major factors that limits. It limits scientific progression. It limits our understanding of problems. A great thing to break down silos is to talk to children. Very often, children ask naive questions. The questions are very poignant.

My youngest son is no longer a child. I, very often, speak to him. His first question is, “Why are you doing it? What is the reason?” Whereas if a scientist asked me that, I’d say, “That’s an insulting question. It’s obvious why I’m doing it.” It’s a very important question. Go back to basics. Why are you doing this? The other thing is the need to not necessarily stick your head in deep into a problem. To walk back a few steps, turn around. Look at it and say, “Why is this problem here? What’s its evolutionary context?” That’s something that comes out of breaking down silo walls.

An Experiment With Light And Bees

It’s very hard for me. There’s so many places where I can start this conversation. I’m going to start it in an unexpected place. A very good way of looking at it is what would we be like 200 years back? Two hundred years back, that’s before electricity. Even so, there wasn’t any incandescent lamp yet. There were candles. Maybe there was fire.

Two hundred years ago, most of us spent a lot more time out. We were walking around in the light when there was light. We live in different countries. You guys may not have the same amount of light. I’m in California. Some people are in better places still for light. People spent a lot of time outside. They got the full spectrum of the sunlight. There was nothing blocking it much. That’s another subject altogether.

Whatever benefit we get from the full spectrum of light, which we will cover, obviously, we all got. We woke up in the morning. We got outside. It’s similar to when you go camping, if you will. You open up the tent, you’re outside. That’s it. That’s what you do all day, then came the night. Sunset. It’s dark. What do you do? You light a fire a little bit. There’s a candle. You go to bed. You go to bed in a dark environment.

Two hundred years ago, that’s an indication of maybe what our body has been needing for a very long number of years. Here comes the electricity. We have electricity around. We have the invention of the light bulb. It’s an incandescent light bulb. We live like this for a long time. Literally in the last few decades and not more than that, energy efficiency starts to take this central role.

The incandescent lamp is too hot because it wastes energy that we can’t even see because it’s long infrared. We have those LEDs. We have these little devices that you and, I believe, I are lucky to have been born and have grown up with nothing like this. If I had to guess, we grew up in a different country. I’m guessing as a child, you played outside a lot with your friends.

Most of the time.

Your mom had to call you for dinner. You reluctantly went something like that. Me too. I feel very fortunate. My children who are now 21 and 23 already got these. We fought the hard fight. We only got them to start using it at age twelve. I consider it a huge achievement because many children are at age 2 or 3. That’s the babysitter.

We used to have windows that could open. I was just in Nashville, Tennessee, studying a nice hotel. You can’t open the windows. You cannot. I was on the 16th floor. They don’t want you to jump. We can see that it’s getting fast. It’s a snowball that’s rolling down the hill very fast. I’m going to roll back a little bit. I’m going back to a point of research that you did in your lab that everyone I interview mentions. We got to talk about it. It’s the red light before the meal and the glucose spike in its effect. Can you tell us about this experiment?

For this, we need to introduce the platform of mitochondria. Mitochondria, you’ve got hundreds if not thousands of them in every cell. They provide you with all the energy that you need to do things. My example is kicking your legs out of bed in the morning. They produce vast amounts of energy. To produce that energy, they themselves need to consume glucose. If we work them hard, like you drive your car hard, it uses more petrol.

You work your mitochondria very hard, which you can do with certain long wavelengths of light, they consume more glucose. One way that you can moderate your blood glucose levels, which obviously are critical for trying to stay away from a pre-diabetic or a diabetic state. It’s to make your mitochondria work harder. You can do it very simply. You can do it with long wavelength light. It’s terribly effective. It doesn’t solve all our problems because controlling your blood glucose is multifactorial.

One way to moderate your blood glucose levels, which are critical for trying to stay away from a pre-diabetic or a diabetic state, is to make your mitochondria work harder. Share on X

You should be going out for a walk. You should burn that energy as well. It wasn’t a surprising result. Its magnitude was surprising. That was giving people blood glucose tolerance test, which is disgusting. Drinking a load of glucose and then pricking your finger all the time. We found if we just expose them to long wavelength light, deep red light, the blood glucose did not spike in the same way. It was around 20% reduction.

One of the key things about blood glucose and its damage is not necessarily how high it is. It’s spiking, that spike. We took the top off that spike. That was very clear. That was an experiment where I had to find subjects. It’s very difficult to find subjects to do something like that. We also put a tube up their nose to measure their oxygen consumption.

We’ve moved on a long way. By changing the light bulbs in environments, we’re doing the same thing. If we put light bulbs into environments that are rich in long wavelength light. We say to people, “Get on with your life. Get on with it. Go outside, come in.” If we do that over a period of weeks, we bring their blood sugars down. It’s a translation from a relatively tight experiment in a laboratory environment to the real world, which is what we’re trying to do all the time. Let’s translate to the real world.

To have lighting that has long wavelength light in it has multiple benefits. One clear benefit is it reduces your blood sugars. It’s very clear. I was frightened to do that experiment. It was someone else who suggested the experiment to me. What we did, I know it’s going to be difficult to get subjects, is we got a beehive. We took the bees. We made the bees do a glucose tolerance test, which is we starve them overnight. In the morning, we gave them a drop of glucose.

We either put them under red or blue light. They don’t have blood. They’ve got something called hemolymph. We pulled off one of their antennae and squeezed them a little bit so the hemolymph came out. One of those little stick things that we all use to measure our blood glucose, we did that. The bees that had red light, their blood sugars were low. The bees that had blue light, their blood sugars were high. I said, “Fine. I believe it now. Let’s do it in the humans.”

Wouldn’t it have been an interesting thing to also have a third group of bees with no light? No special light. No blue. No red.

I agree. It was a spontaneous experiment because I did it quickly and ruthlessly. I got a whole bee colony delivered for about $75. I’ll be straight with you. It was fun as well. It was just fun getting these results quickly. I would have probably done lots of different things with it. I would have done it at different times of day. I would have had bees kept in the dark. I’m not going to start trying to grab hold of a bee in the dark though. Try and hold it down and pull one of its antennae off. So far, I can say I’ve worked on bees and I’ve yet to be stung.

The Impact Of Red Light On Your Body

Fair enough. When you applied, you said the longer wavelengths, clearly, it would be the red in our discussion. The infrared frequencies, the wavelengths are even longer. Does it mean the red had the beneficial effect on glucose spikes or the infrared component also had something to do with it?

The current data that’s coming out is that there is a whole range of wavelengths that have an effect. Some of them, you can just about see. They’re on the edge of human perception. Some of them are in the infrared that you can’t see. Both of them can have an effect. There are some that are more effective than others. There are some that are relatively unaffected.

The point is that it is not specifically about red that you see, or about infrared that you do not see. There’s something else in the mix there. Even with some wavelengths that don’t appear to be incredibly effective, there is still a move in the right direction. I’ve only got so many heartbeats left so I’m not going wavelength by wavelength to find them exactly. The point is we know the wavelengths we’ve tested. We’ve tested the ones that we’re talking about in office environments. They are infrared.

You cannot see the light that is having an effect on you. That’s important for me because I want people to walk into rooms where they don’t realize there’s lots of infrared. If it’s red, your world is full of red. That’s not going to help you. It’s not going to help you feel comfortable about the world. If we can use the infrared that you can’t see, and we work a lot around 800 nanometers, you don’t see it. It has a biological effect. It doesn’t disturb your life.

Going back to that experiment for just a second, when you applied the longer wavelengths, which in the experiment that you had was mostly red. Maybe 670 nanometers. Did you apply it from a panel?

No, we applied it from a series of LEDs that were embedded into a bulb. We didn’t use one of those big red-light panels. In many ways, what we’ve been doing is we’ve been using less and less light to get the same effect. Less energy, more economic to use. We generally find those big panels just push out too much light. You don’t need it. I did discuss this with a red-light panel manufacturer.

I said, “These things are pushing out too much red. I’m uncomfortable. I don’t know what’s going to happen in five years with your body absorbing all this restrictive light. You can get the same effect with far lower energies.” His response was, “If I’ve got a bright panel or a dim panel, which one do you think people are going to buy?” My position is that we’re getting fantastic effects with very low energy levels. There’s no need to have big panels. That also means lower energy, smaller units.

Effects Of Natural Vs. Artificial Light

I’m going to ask you a two-pronged question. Number one, even though I come from an engineering background. I solve problems like an engineer. That way, I have always learned to listen to my so-called gut, my feeling. In the big excitement about red and infrared light panels, I bought a pretty sturdy, long panel that can cover my whole body if I step away just a little bit. It’s by platinum LED. It was approved by some of the experts.

Something in me didn’t let me want to use it. I use it maybe once or twice. You’re right. It floods you with intense red light. You can see the infrared. Here comes the second prong of the question. Your glucose tolerance test and the spike research made so many people buy little panels. They say, “When I have my meal, I put a red panel in.” That’s you. You inspired a lot of people. My question here is, why do we need a panel? Which could come with all kinds of leakages, and who knows what kind of faults, when we can simply step into the natural daylight.

I’m 100% behind the idea of stepping outside. Natural light. You look at the spectrum of sunlight and you think, “We can create that with all these engineering systems.” In fact, I’ve never seen anyone do it properly. We’ve got this joke in the lab that is doing the rounds quite strongly, which is, “If you want good mitochondrial health, the passport to that is get a dog.” You get a dog. You’ve got to go outside two or three times a day.

If you give a high dose of red light, it will only work for a relatively brief period of time. Share on X

Red-light panels or the use of red-light, is a sticking plaster that can be used in urban environments where people spend 95% of their time in buildings. It is only a sticking plaster. It is not the solution. The solution is daylight. For millions of years, you’ve evolved under daylight. I want to add one thing here, which was Scott Zimmerman’s idea. It was great because everyone thinks a bit differently.

I said, “Scott, I’m not very happy about these panels and all these red lights.” Scott and Bob together came up with the idea that you’re overcharging the system. We’ve known for years that if you give red light at a fairly hefty dose, it works very well for about 45 minutes and then it doesn’t work very well. It’s like the thing is freezing now.

With how mitochondria work, they pass an electron down a pathway. At the end of that pathway, there’s a production of energy. We call it ATP. Scott and Bob both said, “What’s happening with this intense red light is you’re getting traffic jams. You’re trying to push too many electrons down this pathway. It’s getting chock-a-block.”

That simple notion happens to fit the vast majority of the data. It fits it well. That means that there can be benefits from red light. If you give a high dose of red light, it will only work for a relatively brief period of time. We have talked quite a lot to people in things like critical care. We’ve talked to people who, for instance, got to deal with head trauma. It may be the case that if you’ve got someone who has got a very significant problem, that it’s worth putting them on and giving them a very hefty dose of red light.

For you and me and the average person who does not get out very much, you should not have a device that produces a vast amount of red light. In the end, I was going to say, it turns around and bites you. It doesn’t. It just turns around and walks away from you. It’s not beneficial. To have these red-light panels and go in under them for five hours a day or whatever it is, you’re wasting your time.

The research has come to a certain point in 2026. It’ll come to a different point in 2036, obviously, moving forward. One thing that we know is you take the best red light and infrared light usually comes as a little pair panel in the world. It gives you maybe 650 nanometer or 670 nanometer or whatever it is for the red. Maybe 850 nanometers for the infrared. Just two frequencies, sometimes four. When you step outside, you get an infinite number of frequencies. You get 650, 651, 651.5, 661 3/4 nanometers. It’s infinite. That’s what our body has evolved to get.

The nice thing about that type of sunlight is that its spectrum is smooth. It’s a smooth, gentle progression across the wavelengths. I did, at one point, try to create devices that put all these LEDs together in this range. It just didn’t work very well. The only thing I can come away from and say from that is that it doesn’t matter how hard you squeeze them. You’ve got all these little peaks. Mitochondria, you couldn’t fool them. They didn’t like this very peaky spectrum. That was very disappointing.

It was, again, a changer for us. Thinking back, “It’s got to be sunlight. It’s got to be that smooth function if you want to have an effect.” It’s very difficult to generate that. A number of companies are trying to produce phosphors that are wide ranging and very smooth. We’ve looked at quite a few of them. Some of them are, they’re okay. They’re a long way from being perfect.

Why We Do Not Get An Overload Of Sunlight

One thing also that’s interesting, you talked about in your experiments. You have been reducing the intensity until you got to a point where you still get the full effect and the benefit, but at a lower intensity. Which of course, doesn’t overload the system. It’s interesting when we go outside in the sunlight, in terms of the intensity, at least in terms of lux. The sunlight is immensely powerful, far exceeding everything that we have indoors. Yet that doesn’t seem to do any overloading on the system.

Because you’ve got a smooth spectrum that goes from ultraviolet across the visual range into IR. The key thing is that is what you’ve evolved under. It’s the balance within the built environment. The boat’s been rocked. The balance has gone. It is only when you try and create that effect with a small number of LEDs that you start to find that there’s this biphasic effect.

If I take an incandescent light bulb and I run an experiment with you on that, there’s an improvement in many functions. An old incandescent light bulb loads. There’s no biphasic effect. It doesn’t stop working. We can have it on in a room. Basically, it works. The tragedy is we’re getting rid of them. The answer to the LED problem, at the moment, is if we can’t go outside, it’s incandescent light with a smooth energy spectrum.

Scott Zimmerman has been trying in his company called Nira Light, to get to step into both worlds successfully. In other words, design a lamp that will satisfy the energy requirements, but also has a little bit of a wire that will give you the infrared. He tells me that they are tightening those requirements so much and making it so high that he doesn’t feel like they’re going to be able to keep up.

He had a great idea of this combination. You can live in an LED world, but you need to supplement it with some form like halogen or some other form of incandescent. He had a great approach. We can get around it another way, which is what I’m trying to push. The halogens will be around for a while because you have to have a halogen in your oven.

Otherwise, it will melt.

The government can’t get rid of halogens without giving everybody a new cooker. You take a halogen. You run it at low power. If you turn the power, which is what we do in most of our lab environments. If you turn the visible light down, the IR doesn’t come down at the same rate. The light gets very dim, but the IR output is still very high.

You then have very low energy consumption. You have a unit that lasts for years. In the architecture school at UCL, there’s a halogen lamp that’s been there. They say it’s been on for about 4 or 5 years, just turned down. When I go to the architects, they say, “That’s a great idea.” There is this wall that you come across. The mere mention of halogen or incandescent, people get their backs up. What can you say about that?

I want to make it very practical for my readers. We understand, and you say very plainly, that barring being outside in the natural light, you’re inside. Having an incandescent lamp is infinitely better than just a set of White cold LEDs. As you said, there was a limit of time. It’s 2028 that you won’t even be able to get them in the United States. I was hoping with the new health services regime, they would get rid of it, but they haven’t. People that I know are stocking a thousand.

I know exactly the point you’re making. Incandescent light is not exactly the same as sunlight, but it’s very close. The statistics that I love about this is all-cause mortality and that includes cardiovascular disease. It includes cancer. It is significantly lower in people that spend more time outside. Much higher rates of those diseases are found in people that live inside. Incandescent bulbs are not exactly the same as sunlight. It would be great if we had the data on what incandescent bulbs are doing in terms of longevity and all-cause mortality.

Incandescent light is not exactly the same as sunlight, but it is very close. Share on X

If I’m not mistaken, I heard you once say that even in a lab full of LED lights, you brought in one incandescent light. Not even very strong. That’s made a very measurable difference in the vitals of everyone in the room.

This is where I started going south, looking for lower energies. We put lights in that room, which should have made everybody’s vision worse. Very often, we look at color vision as a way of testing things. Color vision uses a lot of mitochondrial energy. They all got better. I’m running around pulling my hair out, what little hair I’ve got left.

We found out that the graduate student made a simple mistake. One bulb in that environment had long wavelength light in it. I look to the politicians who I know will not have incandescent lights back. I’m finding a compromise with them. This is a compromise Scott and Bob Fosbury agree with me on, which is you can have an LED world in the built environment. You don’t need a vast amount of IR to take away that toxic effect. That type of result has come back to us time after time.

University College, where I work, has got a vast building, which is horrible. It’s got no windows. It’s all hard White LEDs. It’s where the architects make their models. It’s almost like an aircraft hangar. There, we went in. We put a few incandescent lights around their desks. We told them to get on with their lives. We left them there for a few weeks. Their color vision improved quite dramatically. We can think about having LEDs as lighting, but we need to have protection in that environment. We can get that from a small number of incandescent or halogens.

We’re just trying to work out what the density of those is we need and how we need to put them around. Infrared light is a little bit unusual because we don’t know how it bounces around. It does bounce around a lot. It’s not absorbed very much by many of the things in our environment. We need to find out where it’s bouncing and how it’s bouncing. The basic point is that we can get these two systems to live together, if we think about it carefully.

That’s a very pacifistic and finding-the-middle-ground way of thinking that you have. You’re not up in arms. “Let’s go and fight the government. Let’s just try to coexist.” We understand about the incandescent. The halogen, can we go a little deeper into the halogen? Not all halogen lights are the same. When you say halogen, can you explain this just a little bit more?

A halogen is just a special type of incandescent. When you’re heating up that coil, it’s got a different way with the tungsten that burns off the element. I’d like to say to people, just in your mind, stick the two together. In terms of biological effect, halogen and bog standard old incandescent light bulbs have the same effect. I know engineers design them in very different ways. Fundamentally, from a biological point of view, they’re both kicking out loads of IR. Both are having biological effects, which are much better than having single LED ranges like 670 nanometer or 850 nanometers. Biologically, there isn’t a difference.

What about the issue of the halogen light, those go on and off? Little things that we can’t even see, but it’s there.

You’ve always got a problem with whatever light source with an actual fact with flickers. Flickers are a nightmare in LEDs. One of the arguments we have with a lot of corporates, people are saying, “Change my lighting. I’m feeling uncomfortable. I can see this flickering.” They come along and they say, “You physically can’t see this flickering.” I say, “It doesn’t matter. That person’s going to take three days off this month. Just from a point of view of saving money, change your light bulbs.”

Flicker can be controlled. It’s harder to control it in LEDs, but flicker, basically, can be controlled. None of these are hurdles that we can’t overcome. Our biggest hurdle that we need to overcome is getting people to believe that they should either change their lighting or supplement their lighting. I don’t know what Scott does. Bob and I have just in our kitchens, we’ve got halogen bulbs turned down very low. I know Bob’s had his halogen bulbs in his kitchens for years. He hasn’t replaced them because he just runs them at low power. We’re behaving in line with the way we’re preaching.

How To Allow Sunlight To Bounce Indoors

There is the issue of, assuming that it’s not winter. There is some sun outside. You can open up a window. You’ll get a lot of light. A lot of those bouncing in the room.

Open it up. In domestic environments, most glass doesn’t block IR. In commercial buildings, it does block IR. That’s an issue. A lot of glass tends to block UV as well. You won’t get a sunburn, generally, very effectively through a window. We were talking about this in the lab. The LED environment is an environment that lacks infrared, which has health implications.

The LED environment also doesn’t have many of the wavelengths in the UV that you need to synthesize vitamin D. We’ve got a double hit here in terms of public health. I live in Northern Europe. I’m not opening the window too often, but open the window. Let the light come in. Let it bounce around. One of the big questions is how much does that bounce around? Bob Fosbury, physicist, deeply annoying very often. He says it’ll bounce around 42.3 times. You don’t know how annoying that is, but I’m not a physicist.

It is fascinating. Even when you step outside into the optimal light, the sunlight, what happens to these photons? How do they get into the mitochondria? He talks about how they bounce around. They bounce in the body back and forth. They get absorbed some time. It’s not like the light comes in and it goes straight to the mitochondria. It bounces around.

We’ve often talked about the fact that if you could put a light probe into the body that was sensitive in the infrared, it would be very bright in there. Very bright indeed. We did an experiment where we stood people outside in sunlight. We measured the long wavelengths coming through their body. There wasn’t much coming through their body, but it was measurable.

At that time, I thought the light’s going to come in. We’re going to measure quite a lot coming out the other side. We missed so much of it because it enters the body, and then it goes all over the place. It’s not going to my radiometer sitting on people’s backs. Maybe if I’d stuck a radiometer probe up their nose or down their throats, I would have found a lot more because it’s bouncing around in there until it finds an absorber.

I want to go a little bit about the circadian timeline. I heard you mentioned before that our bodies receive light, red and infrared especially, in the optimal way in the morning. In the morning, you get a lot of red and infrared if you’re watching the sunrise even a little bit. Beyond the sunrise, you don’t have to. There’s a lot of blue. In the context of the morning, blue is not the villain. Blue is only a villain when it’s by itself.

The LED environment lacks infrared and does not have many of the wavelengths in the UV that you need to synthesize vitamin D. Share on X

In the sunlight, blue is surrounded by everything else. The blue wakes you up. It tells you, “It’s morning time, get up.” We have the central clock. You are saying the optimum time is in the morning. What happens in the afternoon? Somebody is reading and says, “I have a break. It’s 2:00 PM. I have a little time. I’m stepping outside.” What happens then? It’s not as efficient? Can you talk about that?

There was a small group of people working on red light who kicked this off. A lot of them were Australians. Some people got effects. Other people didn’t get effects. We all met at a meeting in Baltimore. I remember we were sitting around drinking glasses of wine. People going, “I don’t see what you’re saying.” We started going through all the things that we did. “What trainers were you wearing that day?” Every random thing.

We realized the people that got effects were tending to do their experiments in the mornings. People got no effects or far less effects were doing their experiments in the afternoons. We went away. We’ve done a whole range of experiments on flies, on mice, and on humans. The result is consistent across species, which is you get a much bigger effect if the light you deliver is in the mornings. The mitochondria start picking up their activity just before perceived dawn.

The mitochondria seem to be getting ready for it. Exposure to long wavelength light can be very effective. In the afternoons and the evenings, it could be the case that you’ve generated quite a lot of energy. Some of that ATP you can store in different forms in ADP. In the afternoon, mitochondria are so complex. They’re doing something different. I always judge they’re doing the ironing. They’re doing the housework. Mitochondria do a lot more than just make energy.

Why the mornings? I’ve always argued that the morning is a very vulnerable time for an animal, whether you’re a fly or you’re a human because you’ve been sleeping. You’ve not been conscious of what’s going around you. Predators could be watching you. We look at other metrics in the morning. What happens? Your hormone state is very different. Your blood sugars tend to peak in the mornings.

Maybe you’re getting ready to run away from something. You need to get on the road. You need to be doing things that highly conserved thing from flies through to humans. There was a colleague of mine who did what appears to be a very successful clinical trial for macular degeneration with red light. I rung him up and said, “Your results are good. I’m impressed with this. When did you do your experiments?” He said, “We had to do them before clinic starts because it’s a war zone here.” Again, experiments were being done in the morning.

It’s terribly interesting that a lot of people in light are very concerned, very unimanual with circadian light. That’s very important, but it’s very different from what we’re doing. The wavelengths are very different. Obviously, most things in animals in the world exist in a circadian framework. That’s true of mitochondria. They are receptive when they are dynamic.

You get a much bigger effect if the light you deliver is in the mornings. The mitochondria start picking up their activity just before perceived dawn. Share on X

Naturally, mitochondria are very dynamic between perceived dawn and about midday. When they’re moving, when they’re producing energy, you can push them hard. In the afternoon, when they’re doing the ironing, or they’re doing their domestic work, you can’t push them. You can’t push them at night. I tried that. My poor lab stayed up. I had people staying up 24 hours a day, testing flies, exposing them to red lights. You just cannot get them to move at night.

That’s understandable. That’s how we are. We are vulnerable when we get up. We have to start the day. We may have to move. We have to do things. Here comes noon. At noon time, normally, depending on the season. We have a lot of spectrums. We have UVB, which will help us add Vitamin D. We have UVA.

We have all the blue. Finally, we still have a lot of red and infrared at noon. We have a lot of it. The proportions are different. Here comes the evening. We still have light around. We didn’t have the sun set yet. When the sunset comes, there’s also an abundance of red and infrared. You can see the red. What happens then?

Everybody working in this field should be saying to every other question, “I don’t know.” Because there are still vast amounts of low hanging fruit here scientifically. There are so many I don’t know. I don’t know how circadian shifts work into what mitochondria are doing. I think that, naturally, our energy supplies peak early in the day.

You’re right. Get to midday. The sun’s right above us, if you’re lucky enough to live in that part of the world. You’re getting a lot of infrared light. Maybe the system has produced a lot of ATP that it’s holding in store. Maybe, but I just don’t know. It’s one of the reasons why we work on humans a lot. We also work on flies a lot. Everything we find in a fly. We find in a human basically.

I can use thousands of flies to do an experiment. However, everybody in this building is fed up with me dragging them into offices, giving them lights, and pricking their fingers or asking them to do visual tasks. Again, that’s a silo thing. Some people spend all their lives working on small issues in mice. To understand this, you do need to look across evolution because this is a very old evolutionary event.

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About Glen Jeffery

Dr. Glen Jeffery, PhD, is a professor of neuroscience at University College London of Ophthalmology and a leading expert on how different colors (wavelengths) of light impact cellular, organ and overall health. His research focuses on how light exposure affect the retina and mitochondrial function. He has pioneered studies showing how specific wavelengths of light, including red and infrared, can improve visual performance and support healthy aging of the eye. His work bridges neuroscience, ophthalmology, and environmental health, emphasizing practical, light-based approaches to protect and restore vision.